Two-way relaying is a new paradigm for wireless communications using relay nodes (RN). In conventional relaying strategies, the RN only processes uplink or downlink data packets at any given time. Thus a full transmission cycle (defined as one complete uplink-downlink transmission) will require four channel resources, e.g., time slots. In two-way relaying, the RN simultaneously processes both the uplink and downlink signals. The RN may first receive the signals from the eNB (downlink (DL)) and from the UE (uplink (UL)). It then combines (e.g., adds) both signals and transmits the combined signals to both the UE and the eNB. The UE and eNB remove the self-interference terms and subsequently decode their intended packets. Therefore, one transmission cycle is performed in two channel resources and spectral efficiency is potentially increased.
Channel estimation for coherent transmissions involves the use of pilot symbols that known a-priori to both the transmitter and receiver. Each terminal (i.e., the transmitter and the receiver) uses this knowledge and the received signals (potentially corrupted with noise) to estimate the channel response using an array of methods, such as least squares estimation (LSE).